What Your Rain Gauge Says About You

The measuring tube from an official CoCoRAHS (Community Collaborative Rain, Hail and Snow Network) rain gauge. There’s nothing in it.

To answer the question implicit in the title: I really have no idea.

But your rain gauge, be it an expensive electronic home weather station variety for which you’ve shelled out many hundreds of dollars or a humble plastic tube that you read manually, will tell you one thing for sure this winter in California: It’s been much drier than normal throughout our rainy season, and it’s dry now.

So far, our backyard gauge has caught 6.83 inches of rain since last July 1 (which is the “rainfall year” that used to be the standard for the National Weather Service in California; a few years ago, the agency switched to the “water year,” which runs from Oct. 1 through Sept. 30. For what it’s worth, I recorded exactly one one-hundredth of an inch (.01 inch) from last July 1 through Sept. 30; the Berkeley normal for that three months totals .31 inch).

Where was I? Right — 6.83 inches of rain since last July 1. The Berkeley “normal” for July 1 through March 8, as calculated for the “official” Berkeley station on the University of California campus, is 21.49 inches. One way to look at that: We’re about 15 inches short of our “normal” wet season rainfall. Another way: We’ve gotten just 31.8 percent of that “normal” precipitation.

I’d love to be able to compare my numbers with that station on campus, which has been keeping records since 1893. But I can’t right now. The Department of Geography employee in charge of the weather station and sending data to the public National Centers for Environmental Information database retired sometime in the last few months, and the most recent available numbers from that station are from last September. I’m told that the later data will be forthcoming … soon.

Since the UC Berkeley info isn’t available, I’ve checked to see what other nearby CoCoRAHS (Community Cooperative Rain, Hail and Snow Network) rain watchers have recorded and compared those to the official Downtown San Francisco record for the season.

One gauge, 1.4 miles to the northwest in Albany, has recorded 6.99 inches since July 1 (.16 inch more than my gauge); another, 1.6 miles to the southwest in South Berkeley, has measured 6.39 inches (.44 less than mine). And San Francisco’s Downtown station, which has the longest continuous rainfall record on the West Coast — going back to the summer of 1849 — has picked up all of 7.41 inches since last July 1, or 39 percent of normal.

A look at the California-Nevada River Forecast Center makes it clear that our local percentages of normal — figures in the 30 to 40 percent range — are pretty typical across our slice of Northern California:

Percentage of “normal” seasonal rainfall recorded from Oct. 1, 2020, through March 8, 2021, by way of the California-Nevada River Forecast Center.

One other observation for now, by way of Jan Null, a former National Weather Service forecast who works as a consulting meteorologist. As he noted last week, California is in its second very dry winter in a row and we have a recent historical parallel, from 2013, that we can use to measure advancing drought effects across the state:

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